Method of manufacture of smokeless powder



Patented Mar. 2%, llg

UNITED STATES 2,lli,257

PATEN METHQD (NF MANUFACTURE e015 SMQKELESS lPQlWlllilER No Drawing.Application January 12, 1938, Serial No. 184,705

1i] Claims.

This invention relates to an improved method of manufacture of smokelesspowder, and more specifically to an improved method of manufacture ofcolloided smokeless powder grains.

Colloided smokeless powder, often called dense smokeless powder, isusually made from nitrocellulose colloided by a volatile, ornon-volatile solvent therefor, or by a mixture of volatile andnon-Volatile solvents. The colloided mixture of nitrocellulose andsolvent or solvents is pressed into strands, which are cut into shortsections known as grains. The grains are treated for removal of solventand moisture, dried, glazed, etc.

Such colloided or dense smokeless powder may, or

may not, contain nitroglycerin.

In order to manufacture a satisfactory smokeless powder, it is necessarythat the solvent and moisture content of the powder, known as residualsolvent, be reduced to an amount within well defined limits for the typeof powder desired. The time necessary for the removal of the solvent orsolvents, the temperature to which the powder may be subjected forsolvent removal and drying, the apparatus required, and the percentageof solvent recovered, are important factors in the ultimate cost of thepowder.

Heretofore, various methods have been used for removing the solvent fromthe grains of dense smokeless powder. In one process, known aswater-drying, the powder grains are soaked in hot water, into which thesolvent diffuses. The powder grains are removed from the water and driedin a current of hot air, to remove the adhering moisture. This processis most frequently used in the case of large grains of smokeless powderfor large caliber guns.

The process most frequently used for drying small grains of powder forsmall caliber guns is known as air-drying. The cut grains, containingsolvent, are exposed on shallow trays in large dryhouses to a current ofwarm air for a long period of time. The warm air slowly removes thesolvent as a vapor, in such dilute form that economical recovery of thesolvent is impossible.

,5 Solvent recovery, without the complete drying of the grains ofsmokeless powder, has heretofore been accomplished by placing the cutgrains of powder, containing solvent, in a closed container. Warm air iscirculated through the powder and 50 passes through a condenser, keptcold by sultable refrigeration, exterior to the powder container. Theair current carries the solvent vapor to the condenser, where thesolvent is condensed to a liquid form and is collected and removed forre-use. The air detrained from solvent vapor is 5 heated up to a pointat which it is capable of reabsorbing more solvent and is again passedthrough the powder grains. This cycle may be repeated indefinitely.

Processes for solvent removal and drying of 10 smokeless powder haveheretofore required from three to flve days and large dry-houseinstallations. In such a process, solvent is recovered, but the powdergrains must subsequently be removed from the container for final drying.Large quantities of powder are exposed to risk of fire in thedry-houses. The passage of warm air through smokeless powder grainsgenerates static electricity, the discharge of which may ignite thepowder-dust attendant to such operations.

The equipment of dry-houses usually consists of wooden trays for holdingthe powder grains during the drying process. Metal trays areundesirable, because of the possibility of friction. Wooden trays areunsatisfactory, due to the pos sible contamination of the powder fromwood splinters. Splinters are difficult to screen from the powder, andcause trouble in the machines used for loading the smokeless powder intoshells. The usual dry-houses are more or less hazardous to workmen, asit is necessary to enter them from time to time to re-arrange the traysor to fill or empty the trays. Attempts to speed up the rate of dryingin such dry-houses by raising the temperature or increasing the airvelocity have not been successful. Such changes result in caking thegrains together, in distortion of the individual grains, and in surfacehardening of the grains, which closes the pores and materially retardsthe removal of the solvent or contained moisture.

I am aware that there has been proposed a method of quick dryingsmokeless powder containing solvent by passing through a mass of grainsof such powder a current of heated steam and air. Such a process givessatisfactory results on most varieties of smokeless powder, but oncertain varieties, e. g., on .30 caliber military powder, it giveshlgher'pressures in the gun than are acceptable, as is evident from thetable below, where A represents a normal .30 caliber smokeless powderand B represents a similar powder dried by the accelerated steam/airmethod of forced drying. The results were obtained in a .30 calibermodel 1906 Winchester velocitypressure gun, using Frankford Arsenalcomponents and 1'23 grain 9 boat-tail bullets.

Charge, Mean velocity Mean pres- ?owder grains foot/seconds sure, lbs.

A l9. 5 2570 46, 500 1B 46. 0 2683 54, 800

I have found that such undesirable, .or even dangerous rises inpressure, even with a slightly reduced powder charge, can he very simplyavoided by accelerated drying of solvent-containing powder by animproved method, consisting in forcing a current of a heated fixed gasand alcohol vapor through the powder, followed icy a current of heatedfixed gas, to remove the last arraaev Percent Nitrocellulose 97Diphenylamine .l Diethylphthalate 11 Potassium sulfate 1 Total 16% To100 parts of the above composition 1 added parts of solvent consistingof ether and ethyl alcohol.

I passed heated air/alcohol mixture through a body of cut grains of theabove solvent-containing powder as follows:

Alcohol Temp 00' Pres- Time Total Besid- Drying used, sure, volaual H5Olbs. {Diet outlet lbs. tiles solvent Alcohol and heated air 40 12 5 s0........... -40 20 s 12 40 44 5 15 4o 51 a 15 to 52 s 15 41 55 s so as52 5 30 a9 55 5 240 40 5e 5 60 4o 58 5 120 40 5s 5 c0 40 5s 5 120 40 as5 120 40 59 5 120 40 so 5 120 40 59 5 120 to 59 s 240 154.34 24hrs 3.312.50 1.31

Heated air only 55 52% 5 15 .1 Do 51 54 5 105' Total Residvolaon] E20Upon completion of the tiles solvent treatment the smokeless powdercontained 3.52 2.38 1.14

traces of alcohol from the powder. As fixed gas This powder (A) wastested in a .30 caliber I may use air, nitrogen, carbon dioxide, and the1906 Winchester velocity/pressure gun, using like. As alcohol, toproduce the vapor, I may use Frankford Arsenal components and 173 grain9 ethyl, butyl, propyl, secondary amyl, tertiary boat-tail bullets, incomparison with anormal amyl, iso-butyl, secondary butyl, and iso-propylpowder (B). The results were as follows: alcohols, but not methylalcohol, because of its solvent action on the nitrocellulose of thepowder o w 6 er Charge, Mean velocity, Mean presgrain. I believe that myuse of alcohol vapor grams foot/Seconds sureilba minimizes the surfacehardening of solvent-containing powders which occurs to some extent A49.5 2,663 49,100 when such powders are treated by a current of B 21654501100 heated air and steam. The surfaces of the powder grains thusremaining soft, escape of the Thus my heated airalcohol process ofaccelersolvent from the interior of the powder grain is ated drying ofsmokeless powder avoids the profacilitated. duction of high breechpressures in rifles.

A further advantage of my improved heat- In a further example of thecarrying out of my (ad air/alcohol vapor process over the heatedprocess, I used a pyro .30 caliber powder, of the air/steam process liesin the fact that when using following composition: the latter processthere is considerable dissolv- Percent lng action of the saltconstituents, e. g., potas- Nitrocellulose 97 slum or barium nitrates,by the water present. Dlphenylamine 1 In all cases of use of theaccelerated steam/air Dtethylphthalate 1 treatment a. considerableproportion of the bari- Potassium sulfate l um or potassium nitrate islost, and in the case of a powder containing potassium sulfate, theTotal--- To 100 parts of the above composition 1 added 95 parts ofsolvent consisting of ether and ethyl alcohol.

I passed heated air/isopropyl alcohol mixture through a body of cutgrains of the above solventcontaining powder as follows:

my application, Serial No. 73,095, filed by me April 7, i936.

What I claim and desire to protect by Letters Patent is:

1. In a method of removing solvent from smokeless powder, the stepcomprising subject- A further advantage of my improved drying process isthat it allows the use of an excess of deterrent solution on the powdergrains in the coating operation, with subsequent recovery of thesolvent, instead of economizing in deterrent solution by using onlysufficient of the deterrent solution to wet the grains of powder, as hasbeen past practice, where solvent recovery in the coatill) ing operationwas impractical. In the use of an excess of deterrent solution, theentire mass of smokeless powder grains and deterrent solution is placedin the drier used in my improved process, and a mixture of alcohol vaporand air at a temperature in accordance with the examples hereinbeforestated, and for a time ashere= inbeiore stated, is passed through thepowder until substantially all the powder solvent and deterrent solventare removed, the powder then heing dried by a current of warm air asdescribed.

I do not limit my process to the treatment of any particular variety ofsmokeless powder, and I may use my process in the drying of single ordouble base powders of any size or shape of granulation. The time takenby my drying treat ment will naturally vary with the size or shape ofthe powder grain, since the larger grains will require a longer time forremoval of solvent than will the finer grains. I do not limit mytempera-=- tures to those siown in the examples, since I may wish tosubject certain powders to a longer time of treatment at somewhat lowertempera= tures, and other powders to a shorter treatment at somewhathigher temperatures. l may treat by my improved process the socalleddeterred or progressive burning powders, l. e., those coated with adeterrent, for example dinltrotoluoLdi ethylphthalate, and the like.

My improved process for removal of solvent may be carried out in anysuitable form or ap paratus in which undried powder grains are subjectedto a current of air and water vapor or steam. Such apparatus may consistoi a column containing the powder, a tank, a box, or any containerthrough which can he passed the alcohol/air current which accomplishesthe dry This application is a continuation=in=part or ing smokelesspowder to the action of a current or a fixed gas and a vapor of analcohol which is a non-solvent for the smokeless powder from the groupconsisting of ethyl, hutyl, propyl, secondary amyl, tertiary amyl,isobutyl, secondary loutyl, and isopropyl alcohols.

2. In a method of removing solvent from smokeless powder, the stepcomprising subjecting smokeless powder to the action oi a heated currentof a fixed gas and a vapor of an alcohol which is a non-solvent for thesmokeless powder from the group consisting of ethyl, hutyl, propyl,secondary amyl, tertiary amyl, isobutyl, secondary loutyl, and isopropylalcohols.

3. In a method of removing solvent from smokeless powder, the stepcomprising sulojectlng smokeless powder to the action of a current ofair and a vapor of an alcohol which is a nonsolvent for smokeless powderfrom the group consisting of ethyl, butyl, propyl, secondary amyl,tertiary emyl, iso-loutyl, secondary butyl, and isopropyl alcohols.

4. In a method of removing solvent from smokeless powder, the stepcomprising subjectlng smokeless powder to the action of a current ornitrogen and a vapor of an alcohol from the group consisting of ethyl,hutyl, propyl, secondary amyl, tertiary amyl, isobutyl, secondary hutyl,and isopropyl alcohols.

5. In a method of removing solvent firom smokeless powder, the stepcomprising suloject-= ing smokeless powder to the action of a current ofcarloon dioxide and a vapor of an alcohol from the group consisting orethyl, hutyl, propyl, secondary amyl, tertiary amyl, isoloutyl,secondary I a3 aiiaaov ing smokeless powder to the action of a mixtureof a fixed gas and a vapor of an alcohol which is a non-solvent for thesmokeless powder, from the group consisting of ethyl, butyl, propyl,secondary amyl, tertiary amyl, isobutyl, secondary loutyl and isopropylalcohols, said mixed gas and alcohol vapor being heated to about 40 C.

3. In a method of removing solvent from smokeless powder, the stepcomprising subjecting smokeless powder containing nitrocellulose,dlphenylamine, diethylphthalate, and potassium sulfate to the action ofa current of a fixed gas and a vapor of an alcohol which is a nonsolventfor the smokeless powder, from the group consisting of ethyl, loutyl,propyl, secondary amyl, tertiary amyl, isoloutyl, secondary butyl andisopropyl alcohols.

9. In a method of removing solvent from smokeless powder, the stepcomprising subjecting progressive burning smokeless powder to the actionof a current of a fixed. gas and a vapor of an alcohol which is anon-solvent for the mokeless powder, from the group consisting of ethyl,butyl, propyl, secondary amyl, tertiary amyl, isoloutyl, secondarybutyl, and isopropyl alcohols.

10. in a method of removing solvent from smokeless powder, the stepcomprising subjecting smokeless powder to the action of a heated currentor" air and ethyl alcohol vapor.

LEAVITT N. BENT.

